Cho 100 ml dung dịch H2 SO4 20% D bằng 1,137 gam trên ml vào 400 gam dung dịch BaCl2 5,2% tạo ra được a gam kết tủa A và dung dịch b Tính khối lượng của kết tủa a và C phần trăm của dung dịch B

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.

i think it's c. if you look search electronic symbol on google and then click on wiki it shows you a